This invention relates to measuring in general and more particularly to an improved measuring device for integral values formed over a time span which is constantly up-dated.
Systems are known in which the object of measurement provides an output in the form of series of pulses, each pulse representing a fixed quantity. For example, a rotating flow meter might output one pulse per rotation with each rotation representing a predetermined quantity of liquid. Staying with the same example, assume that each pulse represents 10 cc. Thus, 100 pulses would represent one liter. Suppose it is desired to determine the flow rate in liters per minute. If one counts pulses for one minute the count will be porportional to the flow in liters per minute after a division by one hundred. For example, if the count is 123 pulses that means that the flow rate is 1.23 liters per minute.
Apparatus for making measurements of this nature has been developed and is disclosed in German Offenlegungsschrift 24 46 602. The incoming pulses are fed to a flip-flop having its output coupled to a shift register which is caused to shift by a clock operating at a frequency which is at least as great as the maximum pulse rate input of the measurement quantity. The incoming pulses representing a predetermined quantity act to set the flip-flop. On the next clock pulse this data is transferred to the shift register and the flip-flop reset. The shift register has a length corresponding to the maximum measurable rate, i.e., if the time span over which the measurement is to take place is one minute and if the clock rate is, for example, 200 pulses per minute, then the shift register would have 200 stages. Going back to the example given, this would mean that the maximum rate of the flow meter which could be sensed would be 200 pulses per meter or two liters per minute. Because the shift register is constantly operating it will give the instantaneous average or integral value at any given time. In other words, it is constantly up-dated. With each clock pulse the one minute time integral of the example is shifted 1/200 of a minute. In order to provide an output which corresponds to what it is stored in the shift register in convenient fashion, the input to the shift register is also coupled as the up count to a forward-backward counter. The output of the last stage of the shift register is coupled as the down count. In this manner, the count in the counter always exactly equals the number of pulses in the shift register. Each time a pulse is taken out of the shift register a pulse is taken out of the counter and each time a pulse is added to the shift register a pulse is added to the counter. The counter output is then used to drive an LED display to give a constant indication of the integral value being measured. In the example given above, the output of the counter could be decoded in a binary to decimal decoder and used to drive a LED display which read directly in liters per minute.
In another similar type of measuring device not all components are electronic. Instead of the counter and display, an electro mechanical device such as a stepper motor is driven in one direction, i.e., forward, by the pulses entering the shift register and in the other direction, i.e., backward, by the pulses leaving the shift register. In this manner the angle of rotation of the electro mechanical device corresponds to the content of the shift register. Again, an output indication such as a reading in liters per minute directly becomes possible.
In both of the above-mentioned devices a shift register is utilized into which the pulses representing a fixed quantity are inserted serially bit by bit with the shifting clock rate constant and at least as high as the maximum pulse rate which is to be received at the input.